AOL sold ICQ for $187.5m to DST back in April - a pittance compared to the $400m it paid for the company in 1998.

But ICQ is popular in Russia, the Czech Republic and Germany, especially among eastern European criminal gangs. One investigator said "Every bad guy known to man is on ICQ", according to the Financial Times.

The paper claims that current ICQ servers based in Israel are occasionally accessed by US investigators seeking transcripts of conversations.

The fear is that this easy access will disappear once ICQ moves to Moscow.

DST owns a stake in Facebook and runs Russia's largest email provider and three of the country's other social networking sites.

Investigators have made their concerns known to the Committee on Foreign Investment, which is run by the US Treasury and has the power to block or change deals it fears will hit national security.

But observers said that any such block would likely have come to light within a month of the deal being announced. Maybe that's why they're talking to the FT instead...

AOL, the US Treasury and Homeland Security departments all declined to comment on the FT's story. ®